Undercover investigators for the environmental group ordered cuts of tuna from three Nobu locations in London and put them through DNA tests that determined several were Atlantic bluefin. The species is listed on the International Union for the Conservation of Nature's red list of threatened species for overfishing.

Nobu does not specify on its menus which species of tuna it serves. Requests for the information by campaigners have been met for several years with a terse "no comment".

Although it is not illegal to serve Atlantic bluefin, also known as northern bluefin, many chefs, including Gordon Ramsay, have dropped it because of concern that fishing is at higher levels than stocks can withstand. At Nobu Berkeley St, which has one Michelin star, investigators asked for Atlantic bluefin (hon maguro in Japanese) but staff told them the restaurant did not stock it.

However, DNA tests proved that the fish they were given was indeed Atlantic bluefin. At Ubon, Canary Wharf, also owned by Nobu, investigators ordered Atlantic bluefin and were served a dish that did not test conclusively either way.

Greenpeace writes on its blog that co-owner Robert De Niro "seems to be angling for the title of ‘Godfather of ocean destruction’" and compares offering bluefin tuna to "serving up rhino burgers or tiger chops."